This invention relates to diplexers suitable for use with addressable converters of television sets for reception of cable television programs, plus reception of telephony and transmission of telephony as well as transmission of signals by a cable for interactive television. More specifically, the invention relates to an arrangement of circuit components including inductors and capacitors of channel filters mounted on a stripline board, enabling a reduction of overall physical size of the diplexer while retaining isolation between transmit and receive channels.
Addressable converters are widely used in the television interconnect boxes by which cable communication is connected to a television set in a person's home. Typically, a cable will carry numerous television programs in different frequency bands, and the converter performs the function of selecting a desired one of the frequency bands to be converted to the frequency of a specific one of the channels of the television set which is designated for reception of the cable programs.
This is an important function for the interconnection box, namely, the inputting of cable television program material to the television receiver. However, it is recognized today that telephony can also be communicated via the cable, and technology is advancing to provide for two-way transmission of telephony communication via cable wherein the telephony would occupy a specific transmit band and a specific receive band. Also, to handle the increased interest in interactive television, it is desirable to provide for an outgoing transmission link to carry signals suitable for interactive response. Accomplishing also the functions of receiving and transmitting audio-visual signals requires a channel via cable communication to fully utilize the interactive capacity of the audiovisual equipment.
Thus, it is apparent that the cable interconnection box for a home television set need provide four different functions, namely, reception of video images, transmission of interactive response signals, reception of telephony signals, and transmission of telephony signals. Such functions require the use of a diplexer enabling the connection of transmission and reception channels operative at different frequencies to a common terminal whereby a connection is made to a cable. Furthermore, the channels require filters to ensure adequate isolation between relatively high amplitude transmitted signals and relatively low amplitude received signals. In addition, it is understood that certain services may be subscribed for by a person to the exclusion of other services. Accordingly, relays need be provided within the circuitry for activating and deactivating such services. The relevant frequency bands are below one gigahertz in frequency and, accordingly, it is contemplated that such circuitry would be constructed primarily of discrete components, while some portions may be constructed from distributed components.
A problem arises in that the construction of a connection box with all of the requisite components of the foregoing filters of a diplexer may require a physical volume larger than that which is convenient for utilization within a television cable connection box. An attempt at reduction of physical space by a close positioning of the electrical components may result in cross talk between channels and coupling within a channel, both of which impair the operation of the circuitry. In addition, there is a requirement for manufacturing that the layout of the electrical components must be such as to facilitate manufacture. Presently available circuitry for use in television cable connection boxes does not provide all of the foregoing features.